I have been reading the book "Perfect practice" by Saul Kirsch. It is excellent. I'm not sure if I really learned anything new, but I am reminded of so much that I had forgotten. Basically, it is a collection of practice drills with some useful tips in the beginning of every chapter. The drills are mostly simple ones that stress the fundamentals of our sport: accuracy, the draw, the reload, movement and transitions. He will tell you as any master or GM will that practicing these basic skills is where it's at.
This book was money well spent. Get yourself a copy.